The invention relates to a method for autotuning of an electron microscope in which a series of images of an object are produced, a defined beam tilt being induced for each of said images in direction which differs for each image, after which a the displacements of the images relative to one another are measured and the displacement information is combined.
The invention also relates to an electron microscope suitable for carrying out the method in accordance with the invention.
A method of this kind is known from the publication "Autotuning of a TEM using minimum electron dose" by A. J. Koster et al in Ultramicroscopy 27 (1989), pp. 251-272. Parameters such as beam tilt, astigmatism and defocus are determined by measurement of displacements of images relative to one another, said parameters being used for controlling the autotuning. It is a drawback of the method disclosed in the cited publication that it is effective only in the case of:
1) low magnifications of the electron microscope
2) high magnifications if the specimens concerned have a transmission function which can be described by means of the "Weak Phase-Object" (WPO) approximation. The WPO approximation deteriorates as the specimen is thicker, and hence does not hold for the vast majority of crystalline TEM specimens.